1. Field of the Invention
The present invention relates to a resistor for use in hydrid ICs and various other electronic devices and a process for producing the resistor. Specifically, the invention relates to a thin-film uniform resistor and a process for producing the same.
2. Description of the Related Art
There have been two basic approaches for fabricating resistors useful in electronic devices such as hybrid ICs and thermal heads. One method is a thick-film process in which a coating of thick-film resistor paste is formed on a substrate which is then fired to make a resistor, and the other method is a thin-film process employing sputtering or other thin-film depositing techniques.
In a thick-film process, a powder mixture of ruthenium oxide and glass frit is dispersed in an organic vehicle made of a solvent and a resin, and the resulting thick-film resistor paste is screen-printed on a substrate, which is then fired to make a resistor.
In a thin-film process, which employs vacuum deposition technology, a thin film of a refractory metal such as tantalum, is deposited on a substrate by sputtering, and a patterned, thin-film resistor is fabricated by photolithographic techniques. This method is used to fabricate some of the thermal heads in current use.
The conventional thick-film process which uses thick-film resistor paste has the advantage of achieving high production rate with inexpensive facilities. However, on account of their large thickness (.gtoreq.10 .mu.m) and because of the lack of homogeneity of the thick-film paste which is made of glass frit and ruthenium oxide powder, the resistors produced by this process have the problem of low stability to an electic field, i.e. their resistance changes sharply when they are subjected to voltage variations.
Furthermore, the thick-film process has the following additional disadvantages; the resistance value of the final product cannot be effectively controlled by adjusting the proportions of glass frit and ruthenium oxide alone, also great variations in resistance will occur, not only because of the difference in the particle sizes of glass frit and ruthenium oxide powder, but also, upon the firing temperature used. Even if the same compositional range and average particle size are used, the value of resistance will differ from one lot to another.
The thin-film process is capable of producing uniform thin-film resistors but, on the other hand, this method requires expensive facilities, and achieves only a low production rate.